There is growing consensus that deposition of insoluble deposits of betaA4 peptide cleaved from the amyloid precursor protein (APP) are central to the pathobiology of AD. Overproduction of APP and betaA4 can result from excess APP mRNA as in patients with Down's Syndrome (DS), APP homozygous transgenic animals and a subset of late onset AD patients. We have shown that APP mRNA abundance and downstream APP synthesis are controlled post-transcriptionally by at least two, 3' untranslated region regulatory elements. The 29 base element (29be) is 200 bases 3' from the stop codon and destabilizes APP mRNA. Recently, we discovered that APP mRNA contains a hitherto unknown stabilizing element located adjacent to and extending 50 bases 3' from the stop codon (50sc element or 50sce). This region is present uniquely in APP mRNAs. At least one cytoplasmic protein interacts specifically with the 50sce. Binding activity was detected in multiple cell lines and primary cells, suggesting widespread distribution. Deletion of the 50sc element accelerated APP mRNA degradation by up to 8 fold in transfected cells and reduced APP production by approximately the same amount. Endogenous, wild type APP mRNA and protein were dramatically reduced in SH-SY-5Y cells transfected with 50sce antisense oligonucleotides or decoy mRNAs containing a single copy of the sense 50sce. Thus we hypothesize that the 50sce also regulates the rate of APP mRNA decay and does so by specific interactions with cytoplasmic binding proteins. We also hypothesize that interference with the 50sc element will destabilize APP mRNA and reduce APP production. Therefore, we propose 1). To identify the essential nucleotides required for the stabilizing function of the 50sc element, 2). Determine if the 50sc element can function alone or does so in concert with other regions of the APP 3' UTR, 3). Identify, purify and clone the RNA binding proteins which recognize the 50sce, 4). Determine if blockade of the 50sc element destabilizes APP mRNA in transformed cells and primary neurons, 5). Produce a knock-in mouse lacking a functional 50sc element. In aggregate, these studies will help unravel how APP mRNA stability is regulated in cells and animal models. This knowledge may facilitate the development of anti-AP .